This study of axoplasmic transport in mammalian nerve is intended to characterize the process of transport and to analyse the mechanism responsible for the phenomenon. Axoplasmic transport requires a continued supply of metabolic energy and, as we more recently found, Ca2 ion is integrally involved in the process. The studies now being carried out are to determine what other components in an in vitro medium are needed to maintain transport. Potassium plays a small facilitating role. Calcium cannot be replaced by Mg2 ion. Vinca alkaloids and maytansine are mitotic blocking agents producing a disassembly of the microtubules, the "rails" along which the transport filaments are postulated to move in our model. These agents are effective in blocking transport and at those concentrations a disassembly of microtubues was shown by a fall in microtubular density. We have also been studying the generality of axoplasmic transport. A fast transport of noradrenaline at the same rate as labeled proteins was found, and for the first time a fast transport of dopamine. Those studies indicated a dynamic turnover of catecholamines in the dense core vesicles as they are being transported down the nerve fibers.